I am FIREd (a bit over 1.5 years now) and check Mint every day and my investments probably every day or two - but at least weekly. I prefer to see what is happening and am able to monitor our spending, make on the fly adjustments and keep an eye out for any fraudulent charges easily.
As far as the investment monitoring frequency: I like to think of it as desensitizing myself to the ups and downs, and so far, that has worked well. I no longer get upset or panic when I'm down - even tens of thousands. Hell, I've lost 50K in a month, and it's just a "oh well, I'll get it back eventually" type of though process now. I don't agonize or over-celebrate the losses or the gains any more - it's all just information to be logged. I like the routine and actual knowing/seeing the day to day, if that makes any sense.